The formation and germination of spores of Bacillus subtilis provides a model for examining intracellular differentiation. In view of the increasing evidence implicating the aminoacyl-tRNA synthetases in developmental processes, it is suggested that a study of their possible regulatory functions in a defined syste should prove to be of major import. Because the degeneracy of the genetic code is reflected in multi-component tRNA species for a large number of amino acids, and because aminoacyl-tRNA synthetases are highly specific for both the tRNA which is acylated as well as the amino acid they activate, it is proposed that the cell, through modification of aminoacyl-tRNA synthetase activity, limits the functional capacity of a particular sub-species of iso-accepting transfer RNA during sporogenesis. Examination for a correlation between synthetase activity and sporulation will be made on three levels. Lysyl-tRNA synthetase mutants will be isolated. Through the use of these and wild type strains the sporulation system will be employed to examine for the appearance of altered lysyl-tRNA synthetase activity. Lysyl-tRNA synthetase mutants will be mapped by transformation to locate amino acid and tRNA recognition sites. Studies will be made on the structure and properties of the sporulation and vegetative lysyl-tRNA synthetase and its role in the regulation of lysine biosynthesis during sporogenesis.